Early Herd Immunity against COVID-19: A Dangerous Misconception
David Dowdy, Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health
Gypsyamber D’Souza, Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health
We have listened with concern to voices erroneously suggesting that herd immunity may “soon slow the spread”1 of COVID-19. For example, Rush Limbaugh2 recently claimed that “herd immunity has occurred in California.” As infectious disease epidemiologists, we wish to state clearly that herd immunity against COVID-19 will not be achieved at a population level in 2020, barring a public health catastrophe.
Although more than 2.5 million confirmed cases of COVID-19 have been reported worldwide, studies suggest that (as of early April 2020) no more than 2-4%3–5 of any country’s population has been infected with SARS-CoV-2 (the coronavirus that causes COVID-19). Even in hotspots like New York City that have been hit hardest by the pandemic, initial studies suggest that perhaps 15-21%6,7 of people have been exposed so far. In getting to that level of exposure, more than 17,500 of the 8.4 million people in New York City (about 1 in every 500 New Yorkers) have died, with the overall death rate in the city suggesting deaths may be undercounted and mortality may be even higher.8